Kimbrell discloses a nuclear reactor including a calandria which is mounted above the upper internals. The control-rod drives are passed through the hollow members of the calandria. The coolant is conducted generally axially (vertically) through the upper internals and it flows transversely past the outer surfaces of the hollow members of the calandria. These hollow members are constructed to minimize the stresses produced by the transverse flow of the coolant notwithstanding that the velocity of the coolant may be high (40 ft./sec.). Failure of the guides in the upper internals and of any control rods or control-rod drives of the reactor is thus precluded. The calandria is at a substantially higher level of the reactor than the outlet nozzles.
While the Kimbrell nuclear reactor is on the whole satisfactory, its operation requires that after passing through the calandria, the coolant must flow through a relatively narrow channel between the calandria and the outlet nozzles. There is a substantial drop in the pressure of the coolant between the region where it leaves the calandria and the region where it flows out of the nozzles. In addition, there is substantial resistance to the inflow of cooling water through the outlet nozzles during an emergency. On the occurrence of a steam bubble, the steam would be collected in the reactor head and calandria and block the natural circulation of coolant through the core, calandria and outlet nozzles.
It is an object of this invention to overcome the above-described disadvantages of the Kimbrell reactor.